Such a module is described in my German main application No. P 27 04 869.7-53, corresponding to my U.S. Pat. No. 4 181 141, issued Jan. 1, 1980. A complete control stage for a pneumatic load (for example a compressed-air cylinder), aside from such a module, also includes a plurality of input units in the form of pneumatic limit switches, which are operated by the load itself upon reaching pregiven positions, or manually operated valves for starting and stopping the load, for switching from automatic to manual control, for initiating an emergency stop, etc. These input units are identified all together also as a command unit, so that a control stage for a load consists as a whole of a universal module and a command unit.
In the case of the universal module according to my aforementioned U.S. Pat. No. 4 181 141, the associated load can be switched off only in such a manner that the bistable storage circuit is returned to its nonactive condition. To again switch on the load the storage circuit must receive a new start signal. However, it would be advantageous for certain uses if it were also possible to cause the storage circuit to become disabled, or dead, or to prevent all together the actuation of the storage circuit of the module. This can for example be the case, in a fixed-cycle control for a device for conveying of workpieces in several independent directions, if a certain module is supposed to work only during the movement of the workpiece in one direction, but not for the return movement of the empty workpiece carrier in the opposite direction or during return movement of the workpiece to the initial position. If one could selectively disable such a module depending from signals which are given corresponding on said module, then the entire fixed-cycle control can obviously be inserted much more flexibly, for example can control both a forward movement and also a backward movement. Since an entire cycle of a pneumatic conveying mechanism is composed substantially of two almost mirrorlike semi-cycles, one could in many cases make do with a module chain which controls only half of the entire cycle, if there would be the possibility to otherwise consider the small differences between the two semi-cycles. In this way, a considerable savings in modules and at the same time in external pneumatic structural elements and control valves, which are associated with said modules, could be achieved.
Therefore the present invention is supposed to further develop a module according to my above-referenced U.S. Pat. No. 4 181 141, so that the possibility of a total dead, or disabled, position exists, even if all external signals which are usually required for enabling exist.
This task is inventively attained with a module according to the present invention.
In the case of the inventive module, the bistable storage circuit (which in my aforementioned U.S. patent is formed by a two-position valve, which has two stable end positions, with two servomotors), is replaced with two two-position valves, which are connected in series along the signal flow path and each have one servomotor, of which the first is initially biased into the closing position by spring force and the one farther along the signal flow path is initially biased into the open position by spring force. The output opening of the second two-position valve is connected to an input opening of a further two-way valve which defines an OR-member, the other input opening of which is connected to the start connecting opening of the module. The output of said further two-way valve is connected to the servomotor of the first two-position valve. Through this arrangement one obtains a separately existing feedback line, which can be interrupted selectively to render the module totally dead, or disabled. If the feedback loop of the bistable storage circuit which is formed by the two two-position valves is closed, then the module operates just like a module according to my above-referenced U.S. patent.
Part of this feedback line is advantageously an external connecting line which is connected to the auxiliary connecting openings of the module, which connecting line can be particularly easily blocked or released, by providing in it a suitable further two-position valve.
If the module is totally disabled by interrupting the feedback line (the associated load is not switched on), one can still obtain, at that connecting opening of the module which makes available the activating signal, a short signal for so long as the starting signal is applied to the module itself. While the disabled module thus does not activate its associated load, it still does not interrupt the chain of the fixed-cycle control.
The additional possibility of a disabling of a module also opens up new possibilities in the external switching for the formation of a control stage together with a corresponding command unit and moreover makes the entire fixed-cycle control neater and simpler.